For the first time in years, Roku Inc. is revamping its entire line of streaming media boxes, keeping only one model. The company is betting big on 4K boxes, which it introduced last year. But it also is aiming for the bottom of the market with a basic $30 high-definition streamer.

Three new video players in the line can stream in 4K (aka Ultra HD), an increasingly popular resolution of TV that has four times the pixels of a 1080p HDTV. Two of those models also support high dynamic range (HDR), a more vivid color palette and contrast range encoded in the newest shows and movies from Netflix Inc., Amazon.com Inc.’s Prime and other services.

The old Roku 1, 2, 3 and 4 have been discontinued. Joining the $50 Roku Streaming Stick on the lower end are two players that max out at 1080p high-def resolution.

The $30 Roku Express is the size of a pack of bubble gum. It has an HDMI port to connect to current HDTVs and an infrared remote. A step-up model, the $40 Roku Express Plus, adds a composite cable port that allows it to be connected to older TV sets that don’t have an HDMI port. (The Roku Express Plus will be sold exclusively in Wal-Mart Stores Inc. locations.)

The 4K models start at $80, a substantial drop from the $130 Roku 4. The new 4K models also are 40 percent smaller than their predecessor.

The Roku Premiere ships with an infrared remote and can handle 4K video at up to 60 frames per second. Roku says it has up to 15 different 4K-capable channels, including Amazon, Netflix, YouTube and Vudu.

The $100 step-up Roku Premiere Plus adds HDR video support plus an Ethernet port and a point-anywhere radio-frequency remote with a headphone jack.

The flagship streaming box, and most expensive model, is the $129 Roku Ultra. It adds a digital audio out port and both a USB port and a MicroSD card slot. It comes with a radio-frequency remote that features a built-in microphone to allow voice controls, and there are game-controller buttons on the back too. It also is the only device in Roku’s new lineup that has a button to locate its remote, should it get lost.

Why so many? A large lineup is good for business because it means more retail shelf space at Best Buy Co., Target Corp. and other big-box stores. Roku says people like having choices. The company also says that while its main competitors, Apple Inc.’s Apple TV and Google’s Chromecast, have outsold it at times, Roku consistently ranks highest in streaming hours.

To benefit from the 4K and HDR video, you’ll need a 4K HDR television. (Technically, it has to support the HDR10 format, but nearly every HDR TV does.)

The funny thing is, most of those fancy TV sets have streaming apps built into their operating systems. So why would anyone who spends $2,000 on a new “smart” TV go spend another $130 on a streaming box? The best reason would be if you aren’t getting what you want on your fancy new 4K TV. Roku already has a huge number of apps. And the chances are great that it will get new channel apps sooner than your smart TV will.

Roku also is trying to be helpful by collecting all the available 4K content into a showcase channel. Usually, it is very hard to find 4K content, even with all of the right subscriptions. Roku has more than 100 channels in its universal search, so it is easier to find exactly what you want.

That said, Roku’s days of selling boxes could be limited, which is why it is focusing more on providing an operating system for TVs. Currently, in the U.S., you can find its software powering sets from Haier Electronics Group, Hisense Electric Co., TCL Corp., Sharp Corp. and Best Buy’s Insignia. A Hitachi Ltd.-branded Roku TV is due out soon.